528 research outputs found
The Light Stop Scenario from Gauge Mediation
In this paper we embed the light stop scenario, a MSSM framework which
explains the baryon asymmetry of the universe through a strong first order
electroweak phase transition, in a top-down approach. The required low energy
spectrum consists in the light SM-like Higgs, the right-handed stop, the
gauginos and the Higgsinos while the remaining scalars are heavy. This spectrum
is naturally driven by renormalization group evolution starting from a heavy
scalar spectrum at high energies. The latter is obtained through a
supersymmetry-breaking mix of gauge mediation, which provides the scalars
masses by new gauge interactions, and gravity mediation, which generates
gaugino and Higgsino masses. This supersymmetry breaking also explains the \mu\
and B_\mu\ parameters necessary for electroweak breaking and predicts small
tri-linear mixing terms A_t in agreement with electroweak baryogenesis
requirements. The minimal embedding predicts a Higgs mass around its
experimental lower bound and by a small extension higher masses m_H\lesssim 127
GeV can be accommodated.Comment: 20 pages, 3 figures; v2: changes in the conventions; v3: more details
on the Higgs mass prediction, version published in JHE
Lessons from the decoupling limit of Horava gravity
We consider the so-called "healthy" extension of Horava gravity in the limit
where the Stuckelberg field decouples from the graviton. We verify the alleged
strong coupling problem in this limit, under the assumption that no large
dimensionless parameters are put in by hand. This follows from the fact that
the dispersion relation for the Stuckelberg field does not have the desired z =
3 anisotropic scaling in the UV. To get the desired scaling and avoid strong
coupling one has to introduce a low scale of Lorentz violation and retain some
coupling between the graviton and the Stuckelberg field. We also make use of
the foliation preserving symmetry to show how the Stuckelberg field couples to
some violation of energy conservation. We source the Stuckelberg field using a
point particle with a slowly varying mass and show that two such particles feel
a constant attractive force. In this particular example, we see no Vainshtein
effect, and violations of the Equivalence Principle. The latter is probably
generic to other types of source and could potentially be used to place lower
bounds on the scale of Lorentz violation.Comment: 18 pages, 1 figure. Version to appear in JHEP. Conclusions with
respect to strong coupling modified - our strong coupling analysis does not
apply to a low scale of Lorentz violation. Expanded Equivalence Principle
violation discussion, noting it presents a challenge to low scale Lorentz
violation, exactly the scenario designed to cure strong coupling. Other minor
corrections and references adde
Smooth tensionful higher-codimensional brane worlds with bulk and brane form fields
Completely regular tensionful codimension-n brane world solutions are
discussed, where the core of the brane is chosen to be a thin codimension-(n-1)
shell in an infinite volume flat bulk, and an Einstein-Hilbert term localized
on the brane is included (Dvali-Gabadadze-Porrati models). In order to support
such localized sources we enrich the vacuum structure of the brane by the
inclusion of localized form fields. We find that phenomenological constraints
on the size of the internal core seem to impose an upper bound to the brane
tension. Finite transverse-volume smooth solutions are also discussed.Comment: 1+14 pages, 2 figures; section 2.3 improved, typos corrected and
references added. Published versio
MSSM Electroweak Baryogenesis and LHC Data
Electroweak baryogenesis is an attractive scenario for the generation of the
baryon asymmetry of the universe as its realization depends on the presence at
the weak scale of new particles which may be searched for at high energy
colliders. In the MSSM it may only be realized in the presence of light stops,
and with moderate or small mixing between the left- and right-handed
components. Consistency with the observed Higgs mass around 125 GeV demands the
heavier stop mass to be much larger than the weak scale. Moreover the lighter
stop leads to an increase of the gluon-gluon fusion Higgs production cross
section which seems to be in contradiction with indications from current LHC
data. We show that this tension may be considerably relaxed in the presence of
a light neutralino with a mass lower than about 60 GeV, satisfying all present
experimental constraints. In such a case the Higgs may have a significant
invisible decay width and the stop decays through a three or four body decay
channel, including a bottom quark and the lightest neutralino in the final
state. All these properties make this scenario testable at a high luminosity
LHC.Comment: 28 pages, 18 figures; v2) Discussion on point C removed for
conciseness, minor changes in the text to match the published versio
Flavour physics constraints in the BMSSM
We study the implications of the presence of the two leading-order,
non-renormalizable operators in the Higgs sector of the MSSM to flavour physics
observables. We identify the constraints of flavour physics on the parameters
of the BMSSM when we: a) focus on a region of parameters for which electroweak
baryogenesis is feasible, b) use a CMSSM-like parametrization, and c) consider
the case of a generic NUHM-type model. We find significant differences as
compared to the standard MSSM case.Comment: 22 pages, 7 figure
Closing in on Asymmetric Dark Matter I: Model independent limits for interactions with quarks
It is argued that experimental constraints on theories of asymmetric dark
matter (ADM) almost certainly require that the DM be part of a richer hidden
sector of interacting states of comparable mass or lighter. A general requisite
of models of ADM is that the vast majority of the symmetric component of the DM
number density must be removed in order to explain the observed relationship
via the DM asymmetry. Demanding the efficient
annihilation of the symmetric component leads to a tension with experimental
limits if the annihilation is directly to Standard Model (SM) degrees of
freedom. A comprehensive effective operator analysis of the model independent
constraints on ADM from direct detection experiments and LHC monojet searches
is presented. Notably, the limits obtained essentially exclude models of ADM
with mass 1GeV 100GeV annihilating to SM quarks via
heavy mediator states. This motivates the study of portal interactions between
the dark and SM sectors mediated by light states. Resonances and threshold
effects involving the new light states are shown to be important for
determining the exclusion limits.Comment: 18+6 pages, 18 figures. v2: version accepted for publicatio
Use of Data-Biased Random Walks on Graphs for the Retrieval of Context-Specific Networks from Genomic Data
Extracting network-based functional relationships within genomic datasets is an important challenge in the computational analysis of large-scale data. Although many methods, both public and commercial, have been developed, the problem of identifying networks of interactions that are most relevant to the given input data still remains an open issue. Here, we have leveraged the method of random walks on graphs as a powerful platform for scoring network components based on simultaneous assessment of the experimental data as well as local network connectivity. Using this method, NetWalk, we can calculate distribution of Edge Flux values associated with each interaction in the network, which reflects the relevance of interactions based on the experimental data. We show that network-based analyses of genomic data are simpler and more accurate using NetWalk than with some of the currently employed methods. We also present NetWalk analysis of microarray gene expression data from MCF7 cells exposed to different doses of doxorubicin, which reveals a switch-like pattern in the p53 regulated network in cell cycle arrest and apoptosis. Our analyses demonstrate the use of NetWalk as a valuable tool in generating high-confidence hypotheses from high-content genomic data
Brane-World Gravity
The observable universe could be a 1+3-surface (the "brane") embedded in a
1+3+\textit{d}-dimensional spacetime (the "bulk"), with Standard Model
particles and fields trapped on the brane while gravity is free to access the
bulk. At least one of the \textit{d} extra spatial dimensions could be very
large relative to the Planck scale, which lowers the fundamental gravity scale,
possibly even down to the electroweak ( TeV) level. This revolutionary
picture arises in the framework of recent developments in M theory. The
1+10-dimensional M theory encompasses the known 1+9-dimensional superstring
theories, and is widely considered to be a promising potential route to quantum
gravity. At low energies, gravity is localized at the brane and general
relativity is recovered, but at high energies gravity "leaks" into the bulk,
behaving in a truly higher-dimensional way. This introduces significant changes
to gravitational dynamics and perturbations, with interesting and potentially
testable implications for high-energy astrophysics, black holes, and cosmology.
Brane-world models offer a phenomenological way to test some of the novel
predictions and corrections to general relativity that are implied by M theory.
This review analyzes the geometry, dynamics and perturbations of simple
brane-world models for cosmology and astrophysics, mainly focusing on warped
5-dimensional brane-worlds based on the Randall--Sundrum models. We also cover
the simplest brane-world models in which 4-dimensional gravity on the brane is
modified at \emph{low} energies -- the 5-dimensional Dvali--Gabadadze--Porrati
models. Then we discuss co-dimension two branes in 6-dimensional models.Comment: A major update of Living Reviews in Relativity 7:7 (2004)
"Brane-World Gravity", 119 pages, 28 figures, the update contains new
material on RS perturbations, including full numerical solutions of
gravitational waves and scalar perturbations, on DGP models, and also on 6D
models. A published version in Living Reviews in Relativit
f(R) theories
Over the past decade, f(R) theories have been extensively studied as one of
the simplest modifications to General Relativity. In this article we review
various applications of f(R) theories to cosmology and gravity - such as
inflation, dark energy, local gravity constraints, cosmological perturbations,
and spherically symmetric solutions in weak and strong gravitational
backgrounds. We present a number of ways to distinguish those theories from
General Relativity observationally and experimentally. We also discuss the
extension to other modified gravity theories such as Brans-Dicke theory and
Gauss-Bonnet gravity, and address models that can satisfy both cosmological and
local gravity constraints.Comment: 156 pages, 14 figures, Invited review article in Living Reviews in
Relativity, Published version, Comments are welcom
Performance of CMS muon reconstruction in pp collision events at sqrt(s) = 7 TeV
The performance of muon reconstruction, identification, and triggering in CMS
has been studied using 40 inverse picobarns of data collected in pp collisions
at sqrt(s) = 7 TeV at the LHC in 2010. A few benchmark sets of selection
criteria covering a wide range of physics analysis needs have been examined.
For all considered selections, the efficiency to reconstruct and identify a
muon with a transverse momentum pT larger than a few GeV is above 95% over the
whole region of pseudorapidity covered by the CMS muon system, abs(eta) < 2.4,
while the probability to misidentify a hadron as a muon is well below 1%. The
efficiency to trigger on single muons with pT above a few GeV is higher than
90% over the full eta range, and typically substantially better. The overall
momentum scale is measured to a precision of 0.2% with muons from Z decays. The
transverse momentum resolution varies from 1% to 6% depending on pseudorapidity
for muons with pT below 100 GeV and, using cosmic rays, it is shown to be
better than 10% in the central region up to pT = 1 TeV. Observed distributions
of all quantities are well reproduced by the Monte Carlo simulation.Comment: Replaced with published version. Added journal reference and DO
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